1. Field of the Invention
The present invention concerns auxiliary systems for vehicles, especially, but not necessarily limited to, line-haul trucks, and more particularly concerns auxiliary power, heating and cooling.
2. Background Art
A large truck, and especially a class 7 or 8 line-haul truck, conventionally has a main traction engine, typically diesel, for powering a main traction load and also an auxiliary system load, which may include radio, warning light, and driver and sleeper heating and cooling systems. The auxiliary systems load may also include convenience loads, such as a television, a DVD player, a sound system and a computer system, which may be used during rest intervals when the truck is stopped or while waiting in line for loading or unloading.
It is problematic to use the main engine to power auxiliary loads when it is not needed for the traction load. The main engine is much bigger than necessary merely for auxiliary loads. Besides being an inefficient use of fuel, the main engine also emits more combustion byproducts than is ideal for the smaller, auxiliary load. Various attempts have been made to address this problem. However, each approach that has been developed has some disadvantage.
One solution has been to provide a battery-powered auxiliary power system on a line-haul truck. As bad as it may seem to use the main engine merely for auxiliary loads during long rests and while waiting, it may be even worse to depend solely on a battery-powered auxiliary power system. For one thing, this gives rise to a risk that the battery will run down while the main engine is shut down. If this happens, it requires an external source to jump start the truck, which can be expensive and time consuming. In addition, the auxiliary comfort air conditioning system conventionally includes a compressor that is linked to and driven by the main engine. Therefore, in order to supply auxiliary loads by a battery-powered auxiliary power system it is conventional to also provide an auxiliary heating ventilating and air conditioning system that is independent of the heating and cooling systems driven by the main engine. This adds additional weight, complexity and possible inefficiency. Also, in order to power auxiliary loads by an unassisted, battery-powered electrical system, a large, heavy battery is required. This poses additional inefficiency and expense.
In certain situations, such as at truck stops, external electrical auxiliary power and even external air conditioning may be supplied so that a self-sufficient battery-powered system is not required. However, truck stops are not always available. And even when a truck stop is available, there may not always be sufficient hook ups to electrical power or air conditioning for meeting demand.
Another solution that has been tried is to provide some other power source on a line-haul truck for the auxiliary system load, such as a small, independent internal combustion engine. This does reduce emission of combustion byproducts, but ideally such emissions would be zero for the auxiliary systems load during main engine shutdown. Moreover, an arrangement that uses a small internal combustion engine for auxiliary power, like the arrangement of the battery-powered auxiliary power unit, ordinarily includes an independent, auxiliary heating ventilating and air conditioning system, or else the heating ventilating and air conditioning system may not be available at all during rests or while waiting with the main engine shut down.
Another approach has been to replace the truck battery with a compressed air tank and an auxiliary internal combustion engine that drives an auxiliary air compressor, an auxiliary water pump, and auxiliary AC compressor/heat exchanger pump, and also to replace the main engine electric starter with a pneumatic main engine starting system. Guy Willis, “Small Compact Auxiliary Power System for Heavy Duty Diesel Engine,” EP 0784743B1, May 21, 2003. This provides redundancy for part of the comfort air conditioning system rather than for the entire system. That is, according to Willis two compressors are installed in the same refrigerant loop, where one compressor is driven by the main traction engine and the other is driven by the auxiliary internal combustion engine. Again, using a smaller internal combustion engine for air conditioning during main engine shut down reduces emission of combustion byproducts, but such emissions would ideally be zero for the auxiliary systems load during main engine shutdown. Also, Willis does not disclose how two components of an air conditioning/heat pump system are operated when the main engine is shut down. That is, Willis does not address operation of the air blower that delivers warm or cold air to the cab of the truck, nor the heat exchanger air blower for the air conditioning/heat pump system.
Alternatively, two AC compressors have been installed in independent refrigerant loops, but with a shared evaporator air flow system. Giorgio Moffa, “Air-conditioning System for Motor Vehicles, with Two Sparate and Independent Refrigerating Circuits . . . , ” EP1140533B1, Jan. 22, 2003 (“Moffa”), paragraphs 7-8. This gives rise to some of the same questions and issues suggested by Willis.
Yet another approach has been to provide redundancy for only the drivers of the AC compressor. It is not clear whether Moffa mentions this approach in passing. See Moffa, paragraph 2 (describing an AC compressor receiving power from the main engine or from other sources, but not clearly stating whether these are mutually exclusive arrangements or whether the sources are redundant). Further, even if Moffa is alluding to driver redundancy, he does not disclose how such redundancy is achieved. Some mechanism for driver redundancy has been described elsewhere. Shane Blacquiere et al., “Vehicle Battery Charging and Air Conditioning Operating Unit,” U.S. Pat. No. 6,796,367B2, Sep. 28, 2004. However, in the arrangement disclosed by Blackquire et al., a second pulley is merely bolted to the shaft of an AC compressor for connecting a belt to a second driver. Id., FIG. 5. This arrangement may have disadvantages for long-term service.
In another development, a line-haul truck equipped with a fuel cell was shown in May, 2005, at the U.S. Fuel Cell Council's Congressional Fuel Cell Exposition in or near Washington, D.C. News release from Southwest Research Institute, “Fuel cell-assisted truck completes cross-country trek,” May 26, 2005, http://swri.org/9what/releases/2005/FuelCell.htm. This was for an experimental demonstration of fuel efficiency. Id. Some time shortly before or after this Exposition, the truck was driven from California to Virginia. Id. The inventor of the subject matter of the present patent application inspected the truck in California. Certain of the following observations are based on personal knowledge.
The fuel cell for the demonstration truck was rigidly mounted to the chassis of the line-haul tractor. The cost and durability of current fuels cell may not be adequate for long-term, repeated use in the same manner as the fuel cell system was arranged for the demonstration. Current day fuel cells that are widely available include closely spaced, parallel separator plates of graphite or metal coated with gold to prevent reduction of the plates during operation and are fed by hydrogen gas, which is highly volatile. It presents a challenge to adequately secure such an expensive device in this service while at the same time adequately isolating the device from ordinary bumps and jerks encountered in day-to-day operation of a line-haul truck.
Also, the demonstration truck was converted in such a fashion that non-traction loads, which are conventionally supplied while a truck is in motion by the truck's main traction engine, were supplied directly or indirectly by a fuel cell. These included loads such as an air compressor, fuel, water and oil pumps, and radiator fan for processes that are required for braking or in order for the main engine to drive the traction load. Other non-traction loads were for air conditioning (“AC”). This was an extensive conversion and was expensive. For the thousands of line-haul trucks currently in service, it would not be practical to undertake these particular conversions in order to supply some non-traction loads by a fuel cell. For one thing, according to this conversion, the fuel cell operates full time, instead of just at rest stops and while waiting. This tends to use up the life of the fuel cell, which is an expensive device. It also requires a larger supply of fuel for the fuel cell. Also, this particular conversion requires that individual new electric drivers be provided for some of the loads, which is an added expense that would ideally be avoided.
Another issue with the demonstration conversion concerns a belt-drive arrangement on conventional line-haul trucks. That is, the AC compressor, engine cooling water pump and engine cooling fan on such a truck are conventionally driven by the main traction engine via a serpentine belt routed around pulleys on the shafts of the AC compressor, cooling water pump and radiator fan. According to the conversion undertaken for this demonstration, some of loads were driven, via one or more new belts, by a relatively large electric motor. Aside from being an expensive and time consuming modification, this belt arrangement, as well as other modifications performed in this demonstration truck conversion, might have implications with regard to the truck manufacturer's warranty.
Thus, despite all the above attempted innovations, in order to power auxiliary loads on a line-haul truck it is still a common practice to keep the main engine running during rests and while waiting. For this reason, a need still exists for an improved method and apparatus for providing auxiliary power to a large truck.